Small weed patches may be noticed in fields after herbicide application, but they typically do not have a significant impact on the season’s crop yield. As a result, they are usually not treated as a threat to future yields. However, if these patches harbour weed biotypes resistant to one or multiple herbicides, resistance alleles can spread both spatially (via various dispersal pathways, including seed transport by machinery and commodity contamination) and temporally (through seed persistence). This poses a significant threat to herbicide-based weed management. Once these populations spread and cover a large enough area, eradication becomes improbable despite all the resistance management efforts. Therefore, a proactive and collaborative endeavour is needed to detect and manage small and patchy resistant weed populations. In this paper, we review the current potential of weed resistance detection using imagery and molecular markers as well as possible weed management approaches. Finally, we advocate for the use of a combination of these techniques to manage herbicide-resistant weeds when populations are small. This multifaceted approach is presently not applicable to all resistance mechanisms, and all weed species located in any crop, but could initially focus on biotypes and species that are easy to detect and represent the greatest threat.

Herbicide-resistant weeds pose a threat to food production in modern agriculture, causing US$32 billion in crop production losses worldwide. In Michigan, highly troublesome and widespread weeds include waterhemp, Palmer amaranth, common ragweed, and horseweed, with accessions that are resistant to glyphosate (Group 9) and ALS-inhibitors (Group 2), major herbicide sites of action utilized in soybean and corn cropping systems. Molecular assays for rapid resistance diagnostics to confirm the in-field status of herbicide resistance can assist with more effective, timely, and proactive management. In this research, we developed and tested PCR-based assays to identify target site resistance mechanisms to both herbicide groups through Sanger sequencing and EPSPS copy number variation. Nine different SNPs were identified in five ALS positions known to confer herbicide resistance among all species surveyed. Pro197Ser was the most frequent in horseweed and common ragweed accessions, whereas Trp574Leu was the predominant mutation in Palmer amaranth and waterhemp. Four horseweed accessions contained the Pro106Ser mutation in the EPSPS gene, which confers resistance to glyphosate. Additionally, waterhemp and Palmer amaranth had 2–7 and 20–160 copies of EPSPS, respectively. The assays were validated by comparing genotyping of several field-collected accessions of unknown resistance status with known resistant and susceptible accessions. The efficacy of genotyping assays was >98% and required only two days, confirming that molecular assays are a robust tool for rapid resistance diagnostics. These assays can help growers evaluate herbicide resistance status in weed populations within the same growing season, allowing them to adopt effective management practices.

Kochia is a troublesome, multiple herbicide-resistant tumbleweed which infests Prairie field crops. Kochia has developed resistance to systemic, foliar-applied herbicides from groups 2, 4, and 9, leaving only contact herbicides for post-emergence control. Group 14 chemistry is an important mode of action for resistance management. Weed staging considerations are important as recurrent sub-lethal herbicide exposure can increase risk of nontarget site resistance evolution. The study objective was to evaluate loss-of-control and estimate sublethal dosing exposure risk (SLDER) with a contact-type herbicide (carfentrazone-ethyl) based on initial kochia height, leaf number, and branch number. The SLDER from a single application to a single plant was conceptualized to increase due to escaping plant “volume” or immediate flowering. Kochia was only consistently controlled (100% injury) when dosed at ≤5 cm in height. The estimated maximum size for treated kochia was 21 cm in height, 18 branches plant⁻¹, and the maximum accumulated biomass was between 2.6 and 5.1 g plant⁻¹ for models developed using the initial plant height, branch number, or leaf number as predictors. These estimates represent the largest plant escapes, which would be associated with 100% risk through vegetative considerations into SLDER. Kochia plant size for a 5% risk scenario using the SLDER model was 4 cm in height, 0 branches plant⁻¹, and 11 leaves plant⁻¹ when carfentrazone-ethyl was applied at the labeled dosing. Caution is advised when spraying kochia above 5 cm as incorrect staging may lead to sublethal exposure, escape, reproduction, and escalated risk of nontarget site resistance evolution.

In Canada, soybean (Glycine max (L.) Merr.) is primarily cultivated in three provinces (Ontario, Quebec, and Manitoba). Canadian breeders want to expand the current cultivation range to more northern agro-environments by developing early-maturing elite lines while maintaining good seed quality traits. To examine quantitative trait loci involved in 100-seed weight and seed protein, oil, and fatty acid (oleic, linolenic, and linoleic acids) contents, we generated an early-maturing recombinant inbred line population (QS15544_RIL) and an F₂:F₃ (QS15524_F2:F3) population adapted to cultivation zones MGs 00 and 000, and phenotyped them for 3 years and 1 year, respectively. Using two mapping algorithms (Inclusive composite interval mapping and Genome-wide composite interval mapping), we identified a total of 12 major regions that were either associated with QS15544_RIL (five loci), QS15524_F2:F3 (four loci), or both (three loci) populations. Of the 12 identified regions, three (RIL_GM12, RIL_GM16, and F2_GM04.2) were not previously identified and might, respectively, serve as novel sources of regulation for oil content, seed weight, and oleic acid. For the RIL_GM05 locus, we identified two novel variants in Glyma.05G244100/MOTHER OF FT AND TFL1, a gene with a confirmed role in the regulation of oleic and linoleic acid contents. Two of the major loci (RIL_GM04 and RIL_GM16) associated with the 100-seed weight trait and one locus (F2_GM04.2) associated with oleic acid were found to be overlapping three loci (E8-r1, GM16:5,680,173–5,730,237, and E8-r2) involved in early-maturity and/or shorter pod-filling that were previously identified by our group, suggesting possible breeding bottlenecks due to linkage drag or pleiotropic effects.

Winter wheat (Triticum aestivum L.) is a highly competitive crop with the potential to enhance on-farm revenue and reduce reliance on crop protection inputs. The adoption of winter wheat in the Canadian Prairies has varied significantly over recent decades; however, improved weed and disease management practices could facilitate stability of hectares cultivated. To assess current and alternative pesticide management practices, we conducted a study across 15 site-years at four locations over 4 years (2018–2022). Experimental treatments included pre-plant weed management (glyphosate vs. glyphosate mixed with pyroxasulfone + carfentrazone-ethyl), in-crop weed management (no in-crop herbicide vs. fall-applied 2,4-D vs. fall-applied 2,4-D + spring-applied site-year-specific herbicides), and in-crop fungicide management (no in-crop fungicide vs. one prothioconazole + tebuconazole application at Zadoks Growth Stage (ZGS) 60 vs. two prothioconazole + tebuconazole applications at ZGS32 and ZGS60). Pre-plant glyphosate alone and glyphosate tank-mixed with pyroxasulfone + carfentrazone-ethyl exhibited comparable effects on grain yield, quality parameters, and agronomic characteristics. In-crop weed management had no significant influence on these factors compared to the no in-crop herbicide control, suggesting that in-crop herbicide applications are unnecessary due to the high competitiveness of winter wheat against weeds. However, disease mitigation was prudent as single and double application of fungicide increased grain yield while maintaining grain protein concentration levels. A high-yielding, stable system for optimal grain yield typically required pre-plant weed management coupled with two fungicide applications. These observations confirm herbicide inputs can be reduced in a winter wheat cropping system, but disease pressure requires careful cultivar selection with respect to disease resistance as multiple applications of fungicides were needed to optimize grain yield.

Excess phosphorus (P) loading has been identified as an important cause of poor water quality in Lake Simcoe. A small (∼4%) but important source of P is the marshland that was developed for agriculture in and near the Holland Marsh. Applying the optimum rate of P fertilizer is an economical and environmentally friendly approach to crop management. In Ontario, P fertilizer recommendations are made based on the Olsen P soil test that is accredited by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). The current study was a response to concern about high application rates of P fertilizer and grower and industry suggestions that the recommended rates for P were too low. The marketable yield of yellow cooking onions was assessed in relation to different rates of P fertilizer in high organic matter (muck) soils. Organic matter ranged from 38% to 86%. Small- (6 site-years) and large-scale (21 site-years) field trials were conducted in the Holland Marsh area from 2009 to 2011 on muck soils that varied in pre-plant P (17–312 mg L⁻¹). The study demonstrated that there was more plant-available P in the soil than was required for optimum yield in most fields; thus, P fertilizer applications had no effect on marketable yield of the onions. These results supported the OMAFRA P recommendations for onion production on muck soils, especially for soil test P levels over 61 mg L⁻¹ where a response to applied P is rated as “low, rare, or no response”.

Annual canarygrass is highly responsive to chloride (Cl⁻) fertilizer for increasing grain yield. This responsiveness to Cl⁻ raises the question of whether annual canarygrass is similarly responsive to other micronutrients. The effect of micronutrients, Cu, Zn, B, and Mn with the basal rate of N, P, K, S, and Cl⁻, on annual canarygrass was studied using two application methods, soil (sideband at seeding) and foliar (3–6 leaf and flag-leaf emergence). Over 4 years, field research was conducted at two Saskatchewan locations, Indian Head and Melfort using a randomize complete block design (RCBD). A foliar application after flagleaf emergence of either Cu, Zn, or Mn provided the best method to increase the concentration of that micronutrient in the leaf tissue during seed filling. Boron concentrations in the leaf were increased during seed filling by soil or foliar treatments containing B at different site-years. Zinc, Cu, and B application had no impact on grain yield. A foliar application of Mn affected grain yield at one of six site-years and requires further investigation. As expected, soil application of macronutrients + Cl⁻ increased grain yield between 29% and 187% compared to unfertilized treatment in five of six site-years. Melfort in 2015 and 2016 had low levels of tissue Cl⁻ in control treatment. The largest grain yield increases occurred at these sites, suggesting the potential of early season tissue testing in identifying Cl⁻ responsive fields of annual canarygrass. Annual canarygrass is not responsive to Cu, Zn, and B but may be responsive to Mn.

Plant mitochondrial (mt) genomes enable better understanding of cellular processes and phylogenetic relationships. Tea-scented China rose ‘Hume's Blush Tea-scented China’ is the ancestor of the modern hybrid tea rose and has had an important and lasting influence on the breeding of the modern horticultural rose, but a comprehensive description of its mt genome is not yet available. In this study, mature leaves were used to determine the sequence of the rose mt genome. The mt genome of ‘Hume's Blush Tea-scented China’ is a circular sequence 277 730 bp in length and includes 30 protein-coding genes, 19 tRNA genes, and 3 rRNA genes. We analyzed repeat sequences, codon preferences, and RNA editing processes. In addition, we detected the transfer of 25 chloroplast genes to the mt genome, indicating intracellular genes transferred frequently from chloroplasts to mitochondria in ‘Hume's Blush Tea-scented China’. The phylogenetic analysis of the ‘Hume's Blush Tea-scented China’ mt genome and those of 26 other plant groups reflects its taxonomic status. The Ka/Ks of most genes was less than 1, indicating that most coding genes underwent negative selection, while pi was greater than 0.01, confirming highly diverse genetic variation. This work lays a foundation for future investigation of genetic variation in ‘Hume's Blush Tea-scented China’.

The economic viability of using summer-seeded legume cover crops (crimson clover, red clover, and hairy vetch) as a primary nitrogen (N) source for an organic corn (Zea mays L.)–soybean (Glycine max (L.) Merr.)–winter wheat (Triticum aestivum L.) rotation was determined on a sandy loam soil in southwestern Ontario, Canada, by comparing gross profit for organic production (organic sources of N and phosphorus, no herbicides) to conventional production (no cover crops, synthetic fertilizers and herbicides added). Profits were determined for the initial 3-year transition period from conventional to organic production (2015–2017), and for 5 years of certified organic production (2018–2022). During the transition period when conventional crop prices applied to both production systems, organic production profits (CAD $1148–$1869 ha⁻¹ per rotation) were lower than conventional profits (CAD $2126 ha⁻¹ per rotation). During the certified organic period when price premiums were applied, organic soybean and corn profits (CAD $1995–$2274 ha⁻¹ and $2819–$3195 ha⁻¹ per year, respectively) were significantly greater than conventional soybean and corn profits (CAD $536 ha⁻¹ and $1926 per ha⁻¹, respectively). Winter wheat profits were slightly higher for organic production (CAD $426–$825 ha⁻¹ per year) than for conventional production (CAD $371 ha⁻¹ per year). During the certified organic production period, profits from the 3-year rotations were CAD $5533–$6153 ha⁻¹ for organic production, and CAD $2860 ha⁻¹ for conventional production. It was concluded that an organic rotation of corn–soybean–winter wheat/legume cover crop can be economically viable and more profitable than conventional production on sandy loam soil in southwestern Ontario.

Three multiyear studies were conducted in Manitoba, Canada to evaluate the effect of nitrogen (N) fertilizer rate (ranging from 0 to 225 or 0 to 240 kg N ha⁻¹) and its interactions with timing of N application (preplant, split application), cultivar (Russet Burbank (RB), Glacier Fryer (GF), Umatilla Russet (UR)), and moisture regime (irrigated, nonirrigated) on the yield and net revenue (NR) of potato (Solanum tuberosum L.). Based on soil test N, all sites were expected to be N-responsive, with soil test N at most sites ranging from 24 to 45 kg NO₃-N ha⁻¹ to 60 cm and measuring 70 and 117 kg NO₃-N ha⁻¹ to 60 cm at the remaining two sites. Linear and quadratic coefficients of N and irrigation were significant for yield and NR. However, the NR curves for N inputs were relatively flat, and the NRs were only slightly less than the optimal NR within the vicinity of the optimum. Split N applications performed similarly to preplant N, and GF performed better than RB or UR; however, GF optimal economic N rates were about 55% higher than the optimal economic N rates of RB and UR cultivars. Optimal economic N rate for the best potato practices ranged from 157 to 216 kg N ha⁻¹, depending on the studies; or averaging at about 188 kg N ha⁻¹. Adoption of these best N management practices will improve profitability and N use efficiency in potato production and reduce negative environmental impacts.

In Saskatchewan, red clover (Trifolium pratense L.) is often grown for seed production. However, there is no recognized or data supported seeding rate for seed production of red clover in Saskatchwan. The objectives of this study were to identify an optimal seeding rate for seed production and biological nitrogen fixation (BNF) and to examine their relationships under semi-arid conditions. This experiment was conducted under field conditions using six different seeding rates (0.5, 2.5, 4.5, 6.5, 8.5, and 10.5 kg ha⁻¹) at Melfort and Clavet, SK in 2018 and 2019, and seed yield, biomass, plant density, and BNF were measured. In our study, red clover was able to compensate for the range of seeding rates between 2.5 and 10.5 kg ha⁻¹ without seed yield loss and BNF reduction, whereas biomass production and BNF were higher at 4.5 kg ha⁻¹ seeding rate than in 0.5 kg ha⁻¹ at Melfort, but no seeding rate effects were found at Clavet. Regardless of location, biomass was always positively correlated with BNF. However, no association was found between seed yield and BNF. Our results suggest that 4.5 kg ha⁻¹ is ideal for seed production, BNF and biomass production of red clover in Saskatchewan.

AAC Lariat is a hulled, two-row, spring, general purpose barley (Hordeum vulgare L.) cultivar widely adapted to western Canada. It was developed from the cross AAC Synergy/TR09398 made in 2010 and it was evaluated in the Western Cooperative Two-row Barley Registration Test (2019–2020) before being registered in 2022. With its high yield, good standability, and disease resistance, AAC Lariat will offer a good production choice for feed growers across the Prairies.

AAC GN963 is a high yielding great northern dry bean (Phaseolus vulgaris L.) cultivar with an upright, indeterminate bush (Type II) growth habit, early maturity, and a large seed size. Lodging resistance of AAC GN963 is slight improvement compared to AAC Whitehorse, a great northern bean cultivar with predominant commercial acres under irrigation in southern Alberta. The canning and cooking quality attributes of AAC GN963 were similar to the check cultivars AAC Whitehorse and Resolute. AAC GN963 is well suited for commercial production under irrigation in Alberta and Saskatchewan.

‘AAC Choo’ is a spring, two-row, general purpose barley (Hordeum vulgare L.) released by the Ottawa Research and Development Centre, Agriculture and Agri-Food Canada. AAC Choo is high in yield, good lodging resistance, and moderately susceptible to Fusarium head blight (caused by Fusarium graminearum Schwabe). AAC Choo is recommended for commercial production in eastern Canada.